Preparation of Polyurethane Microencapsulated Expandable Graphite, and Its Application in Ethylene Vinyl Acetate Copolymer Containing Silica-Gel Microencapsulated Ammonium Polyphosphate

Polyurethane microencapsulated expandable graphite (PUEG) is prepared by in situ polymerization, and its structure is characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results indicated PUEG is successfully prepared. The microencapsulated expandable graphite (EG) leads to an increase in the thermal stability and the expanded volume. The research compares the influence of an EG/ammonium polyphosphate (APP)/ethylene vinyl acetate copolymer (EVA) system and a PUEG/silica-gel microencapsulated ammonium polyphosphate (MCAPP)/EVA system on the flame retardancy and mechanical properties. The results indicated that EVA/MCAPP/PUEG composite possesses the same LOI value and UL-94 rating as those of EVA/APP/EG composite. However, the EVA/MCAPP/PUEG system can still pass a UL-94 V-0 rating after being treated with 70 degrees C water for 168 h, indicating excellent water resistance. Because of good interfacial adhesion between fillers and the EVA matrix, the EVA/MCAPP/PUEG composite shows better mechanical and dynamic mechanical thermal properties than those of the EVA/APP/EG composite. Moreover, the electrical property and the combustion behavior of EVA composites are investigated.